Method of firing metallurgical furnaces



Jan. 13, 1948. H. G. ELDER mu 2,434,491

METHOD OF FIRING METALLURGICAL FURNACES Filed Oct. e, 1942 I g'gH E wn' I 4# orney.

Patenta-%I aia 1948 METHOD OF FIRZING METALLURGICAL FURNACES Harold G. Elder, Chicago, and John F. Mowat, La. Graxc, lll.

Application October 6, 1942, Serial No. &80,994 V `3 Claims. i o. zin-52 The present invention is a division of our copending application. Serial No. 363336, filed October 29, 1940, now Patent No. 2,343,00 This invention relates to an improved method of operating a metallurgical furnace for heating ingots and the like. 4

various types of furnaces, more commonly called soaking pits, have been heretofore suggested and used for heating ingots and the like. such furnaces are usually heated by meansof burners arranged in the side walls thereof which 'usually burn a rich fuel gas for rlring the same,

such as coke oven gas, natural gas, or oil, with air supplied for combustion in a manner well known to those skilled in the art. While some of these furnaces have been satisfactory in. their operation and use, others have been unsatisactory. and in most furnaces the burne's were so positioned therein that the flame produced thereby was in extremely close proximity to the ingots being heated therein. in such urnaces it was therefore necessary to limit the fiame temperature by carefully controlling the iuel input to the bumers so as to avoid overheating of the ingots and consequent melting or burning of the metal from which the ingots were made which was not only inconvenient and troublesome, but also inemcient and relatively expensive.

Accordingly, it is one of the objects oi the present invention to provide an improved furnace for heating ingots and the like which is simple and inexpensive in its construction and operation and at the same time, a furnace which uses less fuel than any iurnace heretofore suggested or used, thereby resulting in increased efficiency.

It i another object of the invention to provide an improved iurnace for heating ingots and the like in which the time for heating the ingots or articles therein has been reduced to a minimum due to the extremely high rate of heat initially supplied to the furnace.

It is a further object of this invention to provide a i'urnace for heating ingots and the like of an improved construction and an improved and more economical method of firing and Operating' the same. i

various other objects and advantages oi this invention will become more apparent w in the course of the following speclcation, and will be particularly pointed out in the appended claims.

In the accompanying drawin'g there is shown, for ,the purpose of illustration and description, an embodiment which our invention may assume in practice.

` In the drawings:

Figure 1 is a horizontal section through the improved metallurgical furnace or soaking pit of our inventio'n; and

Figura 2 is a vertical section taken on line II-II of Figure 1. i

Referring more particularly to Figure 1 of the drawings, there is 'shown a conventional type circular i'urnace 2 or soaking pit for heating ingots and the like comprising a circular side wall 3,

usually made of refractory brick, so as to furnish a cylindrical-shaped heating chamber 4 therein having a flat hearth 5 arranged centrally thereof upon which the ingots 6 or articles to be heated are placed in special relation to each other as shown in Figura 1. There is arranged in the center of the heating chamber 6 and extending through the hearth 5 a vertically arranged outlet port 'I for the downward removal of the waste gases from the heating chamber. The bottom portion of the side wall 3 of the furnace is extended outwardly therearound a at 8 so as to provide an annular main combustion chamber a between the outer ingots or articles and the inner side of the bottom side wall portions 8 within the heating chamber. There is provided a dome-shaped reiractory top ID which is removable for the purpose of charging the ingot or articles to be heated into the furnace and for removing the same therefrom.

According to the present invention, 'there is suitably arranged at spaced apart intervals around the furnace in the outwardly extending bottom portion -8 of the circular side wall 3 opposite the main combustion chamber 9 of the heating chamber, a plurality of pairs of horizontally disposed bumers !2, namely four pairs in the present instance, and there is arranged between each of the pairs of bumers !2 a horizontally disposed single burner !3. Both the pairs of burners i2 and the single burner i3are arranged preferably in the same plane angularly relative to the circumference of the side wall 3 and substantially tangential to the annular main combustion chamber 9 so as to provide for substantiali'y tangential firing thereof into the combustion chamber whereby the gases will pass through the same in one direction with sufliclent velocity to remain in the combustion chamber for several turns, thus diluting the burning gases with products of combustion and increasing the volume of gas brought to uniform temperature which is finally forced into the center of the heating chamber between and around the ingots &484.491

3 or articles therein by the incoming gases. The stack draft is controlled by means oi' &suitable damper (not shown) which maintains a substantially balanced furnace pressure through the remcval of the products of combustion as 'rapidly as they are formed.

There is arranged directly opposite each of the outermost burners M of each of the pairs of burners [2 in the bottom portion 8 beyond the main combustion chamber 9 and communicating therewith, an enlarged opening or combustion chamber having the outer side wall IS of each oi' them arranged substantially parallel to their respective burners ll at a spaced distance from the main combustion chamber 9 and terminating in a side wall IT which is substantially tangent to the inner side wall of the heating chamber and outer side of the combustion chamber so that the heat produced by the outermost burners H associated with the enlarged openings or 'combustion chambers |5 will be radiated inwardly by the side walls IS and l'l thereof toward the center of the heating chamber so as to heat the outer portions of the articles, as is clearly shown in Figure 1 of the drawings, with the hot gases adapted to circulate and heat those portions of the articles not directly afl'ected or heated by such radiation.

The outermost burners lt associated with each of the enlarged openings or combustion chambers |5 are supplied preferably with a relatively high temperature preheated air draft, preferably from 1600 F. to 2000 F. and the innermost burner I8 of each of the pairs of burners l2 together with each of the single burners |3 is supplied preferably with an unheated or relatively low temperature air draft, preierably 1200 F. maximum. Thus it will be seen that due to the fact that the outermost burners !4 together with the enlaraed combustion chambers I5 associated therewith are located a considerable distance from the ingots, a short sharp flame may be used, and it is permissible to provide a temperature which need necessarily be limited only by the refractories from which the side walls IS and l'l of the combustion chambers l5 are made, thus permittine the use of air preheated from 1600 F. to 2000 F.

During the first part of the cycle, when the urnace is charged either with cold ingots or ingots from which the molds have been recently stripped, and which contain considerable residual heat, it is permissible to carry a higher temperature in the furnace than when the ingots approach the rolling temperature at which they are to be drawn, this temperature varying with the type of steel or other material to be heated from 2200 F. to possibly 2600 F. During this partof the cycle, all burners are used, with the v high temperature air supplied to burners !4.

When the temperature of the ingots or articles to be heated rises, the fuel input to burners |8 and 13 may be reduced, and the greater part of the heating done by means of burners Il. Under these conditions, with little or no heat input from burners I8 and !3, it would be impossible to heat uniformly by convection and conduction. To overcome this objection, the vertical walls IS and erably is accomplished through automatic conl'l are thus provided and so arranged that radiant heat will be supplied backwards to the intermediate ingots, while the hot gases themselves circulate and heat those portions of ingots not directly affected by such radiation.

The operation may be accomplished in several ways, either manually or automatically, but preftrol (not shown). as follows:

A temperature control of any known type may be inserted in the turnace at one or more points adjacent the material being heated to maintain a rate of heat input suillcient to raise the temperature within the furnace at a regulated rate to apredetermined maximum temperature, which temperature is then maintained until the heating cycle is completed, and the ingots or other articles to be heated are ready to be withdrawn from the furnace. The control is arranged to regulate both sets of fuel burners. The outermost burners M, or those associated with" the large combustion chambers will be supplied with air from conventional recuperators or other heat exchangers at a high temperature. while the remainder of the burners, namely burners !3 and s, will be supplied with air at a lower temperature with the air either being heated in an independent recuperator of a smaller capacity or taken from the high temperature recuperator at a point where the air has been heated to the desired lower temperature, but has not remained in the recuperator in contact with the heating elements long enough to attain the 'maximum temperature required for the high temperature burners.

In operation, the control opens the fuel vaives of all burners to the maximum position at thebegi'nnin'g of the cycle. when the furnace is rela- ,tively cool, in order to maintain the maximum rate of heat input. As the temperature of the furnace rises and the ingots begin to heat up, the control, at a predetermined temperature, begins to reduce the fuel admitted to the burners l3 and |8 using the lower temperature air. At the same time, the known fuel-air ratio control, which proportions the fuel and air to all burners, reduces the air required for combustion in proportion to the adjusted fuel flow. Under some conditions, it may be preferable for the temperature control to regulate the amount of air for combustion, in which case the fuel air ratio contro will proportion the fuel to the regulated amount of air. The reduction of fuel to the lower temperature burners continues to a second predetermined temperature, at which point the fuel may be reduced to a pilot flame, of a volume only suflicient to maintain ignition. Instead of reducing the fuel input in this manner, it may be desirable to reduce it independently of the higher temperature, cutting of! fuel at a deflnite rate per unit of time. until the minimum input required by the pilot flame is reached.

During either of these Operations, the high temperature burners il continue to operate at the maximum rate of heat input, until the furnace temperature reaches the predetermined maximum, at which time the control regulates the fuel input to the high temperature burners to maintain any desired temperature until the ingots are ready to be withdrawn from the fumace.

While we have shown and described an embodiment of the present invention, it will be seen that we do not wish to be limited exactly thereto, since various other modifications may be made ;without departing from the scope of the invention. as deflned by the following claims.

We claim:

1. In a furnace of the circular pit type for the hearth in the heating chamber, supplying heat into the furnace and to the articles therein from points outside the circle by introducing a group of streams of a fluid fuel into the heating chamber substantialy tangential to the circular -arrangement of the articles therein with said streams impinging against the side walls of the heating chamber so that the articles are heated from the heat radiated from said walls and by convection from said streams, introducing a second group of streams of a fluid fuel into the heating chamber substantially tangentialto the circular arrangement of the articles therein to supply heat to the articles principally by convection. heating the furnace and articles therein by substantially all of said streams so as to obtain the .maximum rate of heat ,input until thesame have been heated to a predetermined temperature, and finally reducing the fuel input to at least some of the second group of streams and continuing to heat the articles in the furnace with at least some 'of the streamsimpinging against the side walls of the heating chamber so that the articles are heated from the heat radiated from said walls and by convection from said streams until the articles have been heated to a predetermined maximum temperature. V

2. In a furnace of the circular pit type for heating ingots and the like, the method of opa'ating the same which comprises arranging the articles to be heated substantially in a circle on the hearth in the 'heating chamber, supplying heat into the furnace and' to the articles therein from points outside the -circle by introducing a group of streams of fluid' fuel into the heating chambesubstantially tangential to the circular arrangement of the articles therein with said streams impirging against the side walls of the stantially all of said streams so as to obtain the maximum rate of heat input until the same have been heated to a predetermined v temperature, then reducing the fuel input to at least some'of said second' group of streams until the furnace and articles therein have been heated to a seci heat radiated from said walls and by convection heating the furnace and articles therein-by subond predetermined temperature, and finally cony termined nanum temperature.

3. Ina fbi-hace of the circularpit type for heating ingots and the like, the method of Operating the same which comprises arranging the articles th be heated substantially in a circle on the heartlt in the heating chamber. suppyng' heat into the furnace and to the articles therein from points from said streams, supplying the streams with a relatively high temperature air draft, introducing a second group of streams of a fluid fuel into the' heating chamber substantally tangential to the circular arrangement of the articles therein to supply heat to the articles principally by convection, supplying the second group of streams with a relatively low temperature air draft, heating the furnace and the articles therein by means of substantially all of said streams so as toobtain the maximum rate of 'heat input until the same have been 'heated to a predetermined temperature, then gradualiy reducing the fuel input to the streams to which the low temperature air is supplied until the furnace and the articles therein have been heated to a second predetermined temperature at which point the fuel input of said low temperature air draft streams is reduced to a pilot fiame of a Volume only sufficient to maintain ignition, continuing to heat the furnace by means of at least some of thehigh temperature air draft streams so as to obtain the maximum rate of heat input therefrom until the furnace and articles have been heated to a predetermined maximum' temperature, and maintaining the maximum temperature substantialy constant until it is desired to withdraw the articles bein heated from the furnace by regulating the fuel input to said high temperature air draft streams.

HAROLD G. ELDER.

` JOHN F. MOWA'T.

REFERENCES CITED The following references are of record in the file of this patent:

UNTTED STATES PATENTS Number Name Date' 2,124,888 Morton July 26, 1938 1,926,714 Culbertson Sept. 12, 1933 2,276,971 Hoak Mar. 17, 1942 1,186,104 Kelly June 6, 1916 1,545,496 Jacobus July 14, 1925 960,434- Swindell June '1, 1910 2,252,323 Krogh Aug. 12, 1941 1,867,2 21 Hepburn July 12, 1932 2,052,187 Mawhinney Aug. 25, 1936 1,8371179' Kneass Dec. 22, 1931 1,828,373 Mekler Oct. 20, 1931 1,819,560 Klees Aug. 18, 1931 2,051,401 Winterstein Aug. 18, 1936 2308555 Tate Jan. 19, 1943 OTHER REFERENCES Trinks' "Industrial Fu'naces." Volume I I. 2nd edition (pages 325-326) published by John wiley and Sons, New York, N. Y. (Copy available in Division 28.) i 

